Long descents and winding roads consume more than map distance
A route can look short on paper and still be tiring. Long downhill sections and repeated bends add concentration load for the driver and discomfort for sensitive passengers. By afternoon, that extra strain often matters more than the raw number of kilometres.
Before adding a viewpoint, judge whether the stop is actually safe and easy
The main question is not how pretty the stop is. It is whether parking is clear, getting in and out is simple, and the vehicle can rejoin the route without awkward manoeuvres. If the stop requires guessing, reversing or crowding a difficult roadside area, it is not a good trade.
A later dinner and check-in can damage the next day as well
Xinjiang trip fatigue often shows up after arrival rather than on the road itself. A delayed hotel arrival can compress dinner, showers, children's bedtime and senior recovery. One improvised stop late in the day can disturb two half-days instead of one.
The only good extra stop is the one that adds almost no complexity
If the viewpoint is directly on the main route, uses an obvious parking area, needs only a short stay and the group still feels stable, keeping it can be fine. Once it introduces extra detours, waiting or walking pressure, the stronger choice is to close the day cleanly.